Muscle Tissue- 3 Types

Transcription

1 AN INTRODUCTION TO MUSCLE TISSUE Muscle Tissue- 3 Types Skeletal muscle (focus on these) Cardiac muscle Smooth muscle

2 FUNCTIONS OF SKELETAL MUSCLES Produce movement of the skeleton Maintain posture and body position Support soft tissues Guard entrances and exits Maintain body temperature

3 SKELETAL MUSCLE STRUCTURES Muscle tissue (muscle cells or fibers) Connective tissues Blood vessels and nerves

4 Organization of Connective Tissues ORGANIZATION OF CONNECTIVE Muscles have three layers of connective tissues Epimysium: Separates muscle from surrounding tissues Perimysium: Surrounds muscle fiber bundles (fascicles) Endomysium: Surrounds individual muscle cells (muscle fibers)

5 THE ORGANIZATION OF A SKELETAL MUSCLE Figure 7-1

6 ORGANIZATION OF CONNECTIVE TISSUES Endomysium, perimysium, and epimysium come together to form a tendon: attaches muscle to bone Ligament: attaches bone to bone

7 BLOOD VESSELS AND NERVES Nerves Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord) Blood Vessels Muscles have extensive vascular systems that: Supply large amounts of oxygen and nutrients

8 SKELETAL MUSCLE FIBERS The sarcolemma The cell membrane of a muscle fiber (cell) Surrounds the sarcoplasm (cytoplasm of muscle fiber) A change in transmembrane potential begins contractions Transverse tubules (T tubules) Transmit action potential through cell Allow entire muscle fiber to contract simultaneously

9 SKELETAL MUSCLE FIBERS Myofibrils Subdivisions within muscle fiber Made of myofilaments responsible for muscle contraction Types: Thin filaments: actin (protein) Thick filaments: myosin (protein)

10 SKELETAL MUSCLE FIBERS The sarcoplasmic reticulum (SR) A membranous structure surrounding each myofibril Helps transmit action potential to myofibril Forms chambers called terminal cisternae, attached to T tubules Triad: Is formed by one T tubule and two terminal cisternae concentrate Ca 2+ and release into sarcomeres to begin muscle contraction

11 ORGANIZATION OF A SKELETAL MUSCLE FIBER Figure 7-2a

12 SKELETAL MUSCLE FIBERS Sarcomeres Smallest contractile units of muscle There are multiple within a myofibril Forms visible patterns muscle striations Caused by alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

13 SKELETAL MUSCLE FIBERS Sarcomeres Zone of overlap: densest, darkest areas thick and thin filaments overlap The H Band: area around the M line Has thick but no thin filaments changes length during contraction

14 ORGANIZATION OF A SKELETAL MUSCLE FIBER Figure 7-2 b-c

15 SKELETAL MUSCLE FIBERS Sarcomere Function T tubules encircle the sarcomere near zones of overlap T-tubules transmit action potential to terminal cisternae of SR Terminal cisternae release Ca 2+, which causes thin and thick filaments to interact

16 Thin and Thick Filament Structure Thin filaments: F-actin two twisted rows Tropomyosin; prevents actin myosin interaction Troponin: controlled by Ca 2+ Thick filaments: Contain twisted myosin subunits Tail and Globular Head

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18 THE PROCESS Ca 2+ binds to receptor on troponin molecule Troponin tropomyosin complex changes Exposes active site of F-actin Myosin head of thick filament attaches and pulls thin filament.

19 Figure 7-3 SARCOMERE SHORTENING

20 Figure 7-3 SARCOMERE SHORTENING

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23 NEUROMUSCULAR JUNCTION DIAGRAM (Synaptic terminal) Synaptic Cleft Motor End Plate

24 THE NEUROMUSCULAR JUNCTION 1. Action potential travels along nerve axon to the synaptic terminal. 2. Vesicles release the neurotransmitter acetylcholine (ACh) into the synaptic cleft (gap between synaptic terminal and motor end plate)

25 THE NEUROMUSCULAR JUNCTION 3. Ach binds to receptors on the motor end plate of the sarcolemma. 4. Binding results in another action potential that travels through the sarcolemma and down the T-tubules.

26 STRUCTURE AND FUNCTION OF THE NEUROMUSCULAR JUNCTION Figure 7-4 a

27 TENSION PRODUCTION The all-or-none principle As a whole, a muscle fiber is either contracted or relaxed, but Tension (active force) of a single muscle fiber can vary depending on: number of pivoting cross-bridges fiber s resting length at the time of stimulation frequency of stimulation

28 FREQUENCY OF MUSCLE FIBER STIMULATION A single neural stimulation produces a single contraction or twitch. about msec Sustained muscular contractions require repeated stimuli

29 FREQUENCY OF MUSCLE FIBER STIMULATION Three Phases of Twitch Latent period before contraction: The action potential moves through sarcolemma Causing Ca 2+ release Contraction phase: Calcium ions bind Tension builds to peak Relaxation phase: Ca 2+ levels fall Active sites are covered Tension falls to resting levels

30 NUMBER OF MUSCLE FIBERS ACTIVATED Motor Unit: all muscle fibers controlled by a single motor neuron. Multiple muscle fibers are controlled by a single motor neuron Eye = 2-3 muscle fibers Leg = 2,000 muscle fibers

31 NUMBER OF MUSCLE FIBERS ACTIVATED Recruitment smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated Maximum tension = when all motor units reach tension sustained only a very short time

32 Muscle tone NUMBER OF MUSCLE FIBERS ACTIVATED The normal tension and firmness of a muscle at rest Muscle units actively maintain body position, without motion Atrophy: muscle becomes smaller and weaker when not regularly stimulated

33 NUMBER OF MUSCLE FIBERS ACTIVATED Isotonic and Isometric Contractions Isotonic contraction: Skeletal muscle changes length: resulting in motion Isometric contraction: Skeletal muscle develops tension but does not change length

34 NUMBER OF MUSCLE FIBERS ACTIVATED Muscle Elongation After Contraction Elastic forces: The pull of tendons and ligaments expands the sarcomeres back to resting length Opposing muscle contractions and gravity: reverse the direction of the original motion

35 TYPES OF SKELETAL MUSCLE FIBERS Fast fibers Contract very quickly Have large diameter, few mitochondria Therefore: Have strong contractions, fatigue quickly Slow fibers slow to contract, slow to fatigue small diameter, more mitochondria Have high oxygen supply

36 TYPES OF SKELETAL MUSCLE FIBERS The Distribution of Muscle Fibers and Muscle Performance White muscle: Mostly fast fibers Pale (e.g., chicken breast) Red muscle: Mostly slow fibers Dark (e.g., chicken legs) Most human muscles: Mixed fibers Pink

37 PHYSICAL CONDITIONING Muscle Hypertrophy Muscle growth from heavy training: Increases diameter of muscle fibers Increases number of myofibrils Increases mitochondria, glycogen reserves Muscle Atrophy Lack of muscle activity: Reduces muscle size, tone, and power

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